Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 230455
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1155 PM EST Thu Feb 22 2018


.AVIATION...

No changes to the TAFs this forecast cycle as timing of IFR/MVFR
stratus has been largely on track. Latest observation out of Fort
Wayne is now reporting drizzle, so idea is that potential for
drizzle will exist tonight across all of southeastern Michigan.
There remains low confidence in eventual coverage of drizzle
activity. Surface temperatures have continued to run above freezing
for those areas that are under opaque cloud. Thinking remains that
the environment will be marginal for any negative impacts due to
light glazing. Widespread light rain then anticipated for the late
morning. IFR/LIFR widespread will hold through the morning before
breaking up Friday afternoon.

For DTW...Maintained the TEMPO for -FZDZ between 06-10Z with warm
rain after 10Z. Low confidence continues with regards to coverage of
-FZDZ.

/DTW THRESHOLD PROBABILITIES...

* High for cigs aob 5kft

* Moderate for -FZDZ 06-10Z. High for rain after 10z.

&&

.PREV DISCUSSION...
Issued at 939 PM EST Thu Feb 22 2018

UPDATE...

Not planning to make any drastic changes to the forecast for
tonight. Offered thoughts in aviation discussion earlier with more
emphasis on potential freezing drizzle the latter half of the night
versus freezing rain. Even then, low confidence in timing and
coverage of drizzle exists with a lack of activity immediately
upstream. Surface temperatures are expected to be very marginal with
current surface temperatures this evening still running some 2 to 4
degrees above the freezing mark. Dewpoints are in the 20s across the
Detroit Metro area, but wet bulb cooling potential expected to be
minimal as near surface theta e content increases. From this vantage
point, not expecting any significant impacts.

PREV DISCUSSION...
Issued at 315 PM EST Thu Feb 22 2018

DISCUSSION...

Mid clouds stripped away this afternoon allowing temperatures to
reach into the upper 30s to around 40 degrees across most areas. Dew
pts are predominately in the mid 20s. Mid clouds should be returning
this evening, limiting the diurnal fall expected tonight (upper 20s
to lower 30s), as low level warm advection ramps up as well.

Strong upper wave coming out of the Four Corners region, tracking
through southern Minnesota late tonight, with max 6 hr height fall
center tracking through Lake Superior during Friday. Thus, max
forcing/better isentropic ascent displaced to our northwest, but
there looks to be adequate moisture advection/isentropic ascent
arriving close to 12z Friday to support developing precipitation. It
does not appear the surface high over Eastern Canada will put up
much of a fight, and models indicating a real good surge of warm air
in the 925-850 MB layer, rising into the upper single numbers to
near 10 C. Thus, even if surface temperatures are marginally below
freezing, it is not a given the warm drops will freeze on contact.
Either way, freezing threat looks limited/brief early Friday
morning, and certainly not enough confidence to issue an advisory.
If anything, could see a little freezing drizzle with shallow
moisture before 11z, but otherwise latest HRRR keeps it mainly dry
through 11z, and then expect dew pts to rise above freezing, with
temperatures climbing well into the 40s during the day.

Mid level dry slot arriving Friday afternoon will shut off the rain,
with low level cold air then bleeding in Friday night with northerly
drainage flow. Depth of cold air and southern placement in question
on Saturday as baroclinic zone aligns in west-east fashion, with
high pressure (1026 MB) sliding through the northern Great Lakes.
This high will tend to help maintain the low level cold feed during
the day, as precipitation potentially overspreads southern lower
Michigan (see 12z Canadian/Euro). A light wintry mix is not out of
the question, but surface temps likely well above freezing and with
the daytime timing, probably looking at mainly just a cold rain.

Strong low pressure progged to be centered over the UP of Michigan
Sunday morning will pull an occluded frontal boundary across
Southeast Michigan early Sunday. Behind this front, a much drier air
mass will quickly end precipitation as better mixing allows gusty
winds to overspread the region throughout the day on Sunday. High
pressure will then build into the region early next week as upper
level ridging slowly rebuilds over the Eastern US. This will bring a
period of dry, calm conditions to Southeast Michigan through Tuesday
as temperatures remain above average with highs in the mid 40s to
lower 50s while lows fall into the upper 20s to lower 30s. As the
high moves to the Eastern Seaboard by midweek, return southwesterly
flow will advect moisture across the region ahead of the next wave
moving into the central US. Shower chances look to increase starting
Wednesday as temperatures remain above average with highs in the mid
40s to near 50.

MARINE...

Light to moderate flow will dominate through Saturday. Strong east
to southwest wind will develop on Saturday night as a deepening low
lifts toward the Straits. Stability may be sufficient to probhit
gusts to gales on Saturday night, but the gradient will ramp up as
wind turns southwesterly on Sunday. A gale watch may eventually be
needed for the waters of Lake Huron...particularly the central axis
of the Lake including part or all of Saginaw Bay.

HYDROLOGY...

Flood warnings remain in effect for most of the primary river basins
over southeast Michigan. Additional rain on Friday is not expected
to contribute to additional flooding or prolong existing flooding as
amounts will remain generally one quarter of an inch or less.
Another round of rain will then impact the area late Saturday into
Saturday night with perhaps one half of an inch of rainfall falling
in some areas. This may impact river and stream levels to some
degree, but should not exacerbate flooding to any great degree.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

AVIATION.....CB
UPDATE.......CB
DISCUSSION...SF/JD
MARINE.......JVC
HYDROLOGY....JVC


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